Method and apparatus for in-line detection of satellite signal lock

ABSTRACT

A method and system for detecting satellite signal lock in a satellite receiver system is disclosed. The system includes a first filter that isolates a noise frequency from the satellite signal, a second filter that isolates a service frequency from the satellite signal, circuits that derive a value indicative of the difference between a noise component and a service frequency component and output a difference signal level, a first comparator that determines whether the difference signal level is greater than a first threshold level, and a second comparator that determines whether the difference signal level is greater than a second threshold level. The method includes the steps of establishing a first threshold value between a satellite signal power level and the noise power level, combining a value indicative of a noise frequency signal component with a value indicative of a service frequency component to obtain a difference signal value, comparing the difference signal value with the first threshold value, and issuing a command if the difference signal value is below the first threshold value to inform the user of the loss of signal lock.

This is a continuation of application Ser. No. 08/792,048 filed Feb. 3,1997, U.S. Pat. No. 6,029,044.

BACKGROUND OF THE INVENTION

The present invention relates generally to satellite communicationsystems, and more particularly to a method and system for detectingsignal lock between a satellite receiver and a satellite in a digitalDBS system.

Generally, in modem digital satellite communication systems aground-based transmitter transmits a forward-error-coded uplink signalto a satellite positioned in geosynchronous orbit. The satellite in turnrelays the signal back to a ground-based receiver antenna in a separatelocation. Direct broadcast satellite (“DBS”) systems allow households toreceive audio, data, and video directly from the DBS satellite. Eachhousehold subscribing to the system receives the broadcast signalsthrough a receiver unit and a satellite dish receiver antenna.

The typical consumer DBS system consists of a satellite receiver antennawhich includes an e.g. 18-inch parabolic dish and low noise block(“LNB”), and a receiver unit which may include an integrated receiverdecoder module, or “IRD”. The receiver antenna is typically mountedoutside the house, and cables are provided to link the LNB to the indoorIRD and associated equipment (e.g. video display).

Several factors can degrade received DBS signals. For example, thesatellite receiver antenna can accumulate snow, ice, leaves, or otherdebris unseen by the user. Remote blockage may also develop, such asshadowing foliage (e.g. trees). This accumulation or other shadowingobstruction can degrade the received signal strength enough to interruptIRD operation. Furthermore, due to the significant amount of forwarderror correction used, the DBS picture or data quality may not sufferany noticeable decrease although signal strength is continuouslydegrading. When signal strength falls below a certain minimum, thesignal can be completely lost without warning.

Other sources of DBS signal degradation include antenna tracking errorsin mobile installations, such as ships, trains, or automobiles, each ofwhich require constant adjustments to the receiver antenna'sorientation. As with fixed DBS systems, the signal degradation in amobile DBS installation can result in complete loss of signal lockwithout warning.

Therefore, there is a need for an inexpensive and simple method andsystem for automatically detecting signal degradation and for warningthe user when a DBS signal is degrading, to provide an incipient signalloss warning or reaction. There is a particular need for such a methodand system which may be added to existing satellite receiving equipmentwithout modification, e.g. as an “add-on” device.

SUMMARY OF THE INVENTION

The present invention provides an inexpensive and simple method andsystem to detect signal degradation and to warn the user that signalstrength is degrading or has degraded below a given threshold. Thepresent invention may be embodied in a system that processes a portionof the receive antenna/LNB output and splits this incoming RF signal. Ina preferred embodiment, the signal is split into three components, onehaving the majority of the received power and the others having lesserpower. The RF signal in one path (preferably one of the lesser-powerpaths) is passed through a filter that isolates a portion of thefrequency spectrum corresponding at least predominantly to anintelligence carrying or “service” frequency signal, such as a portionof a satellite transponder signal of the DBS system. The RF signal inanother path (preferably also lesser power) is passed through a secondfilter that isolates a portion of the frequency spectrum which containsonly (or predominantly) “noise” signals.

The difference in power between the two filtered signal components isthen detected. For example, the output of each filter is passed to aseparate RF detector. Each RF detector converts the RF signal at itsinput to a DC voltage or some other output (e.g. a digital output) thatis proportional to the input signal power. Scaling (e.g. amplification,attenuation, or digital manipulation) may be used to compensate fordifferences in absolute outputs of the one or more portions of thedevice. The difference between the two power levels is then detected.For example, in one embodiment a voltage corresponding to one of the RFsignals (e.g. non-signal noise power) is passed through an inverter.This inverted signal is then summed with a DC signal corresponding tothe other signal component (e.g. the service frequency signal power). Inthis way, a voltage is obtained which is proportional to the differencein the relative powers of the desired service signal and the noisesignal (the “difference” value or voltage). Finally, the RF signal inthe third path, preferably having the majority of received power, may bepassed unaffected to a receiver (e.g. IRD) for normal processing.

The difference value or voltage can then be passed to a comparator (orseveral comparators) or the like for comparison to one or morepredetermined thresholds. For instance, a difference voltage can becompared to a level corresponding to loss of signal lock. The differencevoltage could also be compared to a level somewhat higher than the lossof signal lock level, relating to a degraded signal or incipient signalloss.

In another aspect of the invention, the system includes a user interfacefor alerting the user of an approaching loss of signal lock. The userinterface may in part allow the user to activate an external device, orotherwise select a corrective measure from a menu of options to curtailsignal loss.

The invention may be further embodied in a method that includes thesteps of establishing a first threshold value (e.g. between therespective levels representative of the satellite signal and the noise),combining a value indicative of a noise frequency signal component witha value indicative of a service frequency signal component to obtain adifference signal value, comparing the difference signal value with afirst threshold value, and issuing a command if the difference signalvalue is below the first threshold value. The command may indicate e.g.that signal lock has been lost. In another aspect of this method, thesteps further include establishing at least a second threshold valuegreater than the first threshold value. The second threshold may be usede.g. to issue a warning that signal lock is degrading and may soon belost.

The present invention thus provides a method and system for determiningwhen a received signal has degraded, or has been lost, by detecting therelative levels of the desired (i.e. service frequency) to background(i.e. noise) signal components present in the signal. In certainembodiments, the method and system allows the user the opportunity totake steps to correct the degrading signal independent of the receiver.The method and system utilize a small number of simple electroniccomponents and do not require a microprocessor (although one may beutilized), thereby allowing the unit to be more reliable andinexpensive. Furthermore, the method and system can warn the user ofsignal degradation and possible loss, allowing the user to takecorrective measures before the signal is completely lost.

In preferred embodiments, the system may be implemented as an add-onaccessory for use with a variety of receivers. In one preferredembodiment, the detection circuits may be housed in a module forinsertion in-line between an LNB and an IRD. A bypass path or throughline may be provided to conduct the majority of the received signalpower directly from the LNB to the IRD. Because the invention operatesto detect signal loss or degradation without requiring analysis ofsignal content or intelligence, the add-on device does not requirecomplex tuners, decoders or error measurement circuits. The device maytherefore in certain embodiments work independently of the IRD, otherreceiving components, or the signal format used for the satellitesignal.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are intended to provide further explanation of the invention asclaimed. The invention, together with further objects and attendantadvantages, will best be understood by reference to the followingdetailed description, taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional direct-to-home DBS satellitetelevision system capable of utilizing the present invention (priorart).

FIG. 2 is a diagram of an embodiment of the in-line detection apparatusaccording to the present invention.

FIGS. 3(A-E) illustrate exemplary DBS broadcast frequencies, andpreferred embodiments for the service signal and noise filtercharacteristics usable in one embodiment of the present invention.

FIG. 4 shows an alternative embodiment of a portion of the embodiment ofFIG. 2, corresponding to the embodiment illustrated in FIG. 3(E).

FIG. 5 shows a user interface screen capable of integration with thein-line detection apparatus of the present invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Referring now to the drawings, and more particularly to FIG. 1, arepresentative digital DBS system 12 capable of utilizing the presentinvention is shown. The DBS system 12 preferably includes a ground-basedbroadcast transmitter 13, a space segment 14 that includes a satellite15, and a ground-based subscriber receiving station 16. In an exemplaryDBS system, the satellite 15 is a geosynchronous satellite, such as theHughes® HS-601™ spacecraft, preferably positioned at a geosynchronousorbital location. The home subscriber receiving station 16 includes anoutdoor receiver antenna 19 including a low noise block (LNB) 20connected to an indoor receiver/decoder box (IRD, not shown) via a cable(also not shown).

The broadcast transmitter 13 receives digitally modulated television oraudio signals and transmits them to the satellite 15. The satellite 15translates the signals to a downlink frequency (e.g. in the Ku band) andtransmits them to the receiver antenna 19 of the receiving station 16for subsequent demodulation. The satellite 15 transmits downlink signalsvia on-board transponders 17 operating at a power level of e.g. 120 to240 watts. The LNB receives the downlink RF signals, amplifies them, andtypically down-converts them (e.g. to the L band). When the downlinksignal from the satellite 15 is received in the receiver antenna 19 withsufficient signal strength to be demodulated, the satellite signal isconsidered to be “locked” with the receiving station 16.

A preferred embodiment of a lock-detect subsystem 55 for monitoringsatellite signal lock is provided as described below. As shown in FIG.2, the outside line 91 from the LNB 20 is connected to the lock detector92 at an input 63. The input 63 preferably feeds a tap or coupler 88. Aline 62 allows a portion (preferably a majority, e.g. 90 percent) of theLNB signal to pass through the detector 92 to the cable 29 and thus theIRD 95 regardless of whether the lock detector 92 or IRD 95 power is onor off. A portion 22 of the LNB signal is fed to a pair of filters 57and 58. Filter 57 is a signal or service frequency filter, and filter 58is a noise frequency filter. Preferably the portion 22 of the LNB signalfed to the filters is a relatively small percentage of the total LNBsignal (e.g. 10 percent). A splitter 21 is preferably used to divide theportion 22 between the respective filters, into signals 23, 24.

In the specific embodiment illustrated, the output of filter 57 ispassed to a radio frequency RF detector 64, which in turn is linked toan adder circuit or summer 59. The output of filter 58 is passed to asecond RF detector 65, and to an inverter 68. The inverter 68 output iscoupled to summer 59. The RF detectors 64 and 65 convert the measuredaverage RF power level outputs of the filters 57 and 58 to obtain tworepresentative output signals, e.g. DC voltage levels. The output signal66 of summer 59 is supplied to one or more comparators, such as a pairof comparators 60 and 61. The outputs 93 and 94 from the comparators 60and 61, respectively, may be functionally connected to one or more ofindicator devices, logic 53, or switch 71.

The filter 57 preferably passes only signal or service frequenciescorresponding to a range of a known service band or channel in theservice spectrum. More than one range or channel may alternatively beincluded. Although preferably only signal or service frequencies arepassed, it should be understood that in certain embodiments a limitedamount of noise may also be passed, so long as the signal ispredominantly comprised of service frequencies.

The filter 58, in contrast, passes a range of noise frequenciescorresponding to a known region in the received spectrum where noservice band or channel is present. Once again, although it is preferredthat filter 58 pass only background noise components, in certainembodiments a limited amount of signal or service frequencies may alsobe passed, so long as the passed signal is predominantly comprised ofnoise (non-service) frequencies.

FIGS. 3(A-E) illustrate preferred embodiments of frequencycharacteristics for filters 57, 58 in the context of a representative Kuband DBS system. FIG. 3(A) illustrates a typical downlink frequencyutilization for a system having a plurality of transponders, each withan assigned frequency band (e.g. 101-108). In the system illustrated,these transponder signals (which may number e.g. 32) are located in a500 MHz portion of the Ku band, e.g. between 12.2 and 12.7 GHz. As isknown in the art, the signal carrying capacity within this assigned bandcan be increased by utilizing polarization multiplexing, e.g. right handcircular polarization (RHCP) and left hand circular polarization (LHCP).In the system illustrated, frequency bands for those transpondersassigned to RHCP (101, 103, 105 and 107) are interleaved in a“staggered” fashion with those assigned LHCP (102, 104, 106 and 108). Ingeneral, the center frequency of a RHCP band (e.g. 103) corresponds tothe center of a guard band lying between two adjacent LHCP transponderfrequencies (e.g. 102, 104).

In manners known in the art, the LNB receives both RHCP and LHCPsignals, but is configured electronically (or, in less preferredembodiments, mechanically) to discriminate and process only one of therespective polarizations. This signal is then typically down-convertedin frequency to a 500 MHz portion of e.g. the L band, such as thespectrum between 950 MHz and 1.45 GHz. The LNB output will thereforecorrespond to the signal shown diagramatically in FIG. 3(B) if the LNBis configured to process RHCP signals, or the output shown in FIG. 3(C)if the LNB is configured to process LHCP signals.

The filter characteristics for filters 57, 58 are preferably chosen tosupport this frequency/polarization utilization scheme, permitting thelock-detect system 55 to function with standard equipment in commercialproducts and support their complete functionality, including LNBselection of RHCP or LHCP signals. FIG. 3(D) illustrates preferredfilter characteristics. The signal or service frequency filter 57 has apassband center frequency 121 which preferably corresponds to theapproximate middle frequency between the outer boundary (e.g. 124) of aselected RHCP transponder frequency band (e.g. 117), and thecomplimentary outer boundary (e.g. 123) of an overlapping LHCPtransponder frequency band (e.g. 118). By selecting a filter passbandcorresponding to an “overlap” between the staggered RHCP and LHCP bands,a single filter (as illustrated in FIG. 2) can function to isolateservice frequencies regardless of whether the LNB is processing RHCP orLHCP signals. In a known DBS system utilizing 32 equal transponder bandsstaggered between 12.2 and 12.7 GHz, the center frequency of the signalor service frequency filter 57 may be chosen to lie within the region ofoverlap between any adjacent LHCP and RHCP transponders, e.g. atC_(f)±7.29 MHz, where C_(f) is the center frequency of a particulartransponder.

The bandwidth or passband characteristic 120 of filter 57 is preferablyselected to reduce susceptibility to variations in transponder roll-offcharacteristics from one transponder to the next, as well as variationsin LNB local oscillator frequency. In general, it is desirable toprovide a passband and roll-off characteristic to maximize the amount ofsignal (whether RHCP or LHCP) which is passed, while minimizinginclusion of noise signals in the adjacent guard band. In therepresentative system previously described, a standard 6 MHz widebandpass filter may be used. Such filters are common in the cableindustry.

Referring still to FIG. 3(D), the noise frequency filter 58 preferablypasses a band of frequencies lying above (or below) the highest (orlowest) transponder band, and also below (or above) any neighboringspectrum allocation. By way of specific example, a known Ku-band DBSsystem operates within a 500 MHz band between 12.2 and 12.7 GHz. The LNBdownconverts the signals to the L-band, between 950 and 1,450 MHz. Aguard band of approximately 12 MHz separates the highest (and lowest)transponder band from the upper (and lower) limits of the assignedspectrum. This separation provides protection from interference byneighboring services, and should contain no intelligence-carryingsignals.

Accordingly, it is preferred to select the passband characteristics ofthe noise filter 58 to correspond with one or both of these guard bands.A representative characteristic 130 is shown, with center frequency 131.The bandwidth of filter 58 is not critical (although preferably narrowenough to exclude signal frequencies). It may also be desirable toselect a passband which is easily and inexpensively implemented, andwhich results in noise power levels having a value (when discriminated,as discussed below) in an appropriate range for ease of processing. In apreferred embodiment, the standard 6 MHz bandpass filter common in thecable industry may similarly be employed. As shown, the noise filter mayhave a greater or lesser passband (e.g. as shown in alternative 132), ornoise signals could be derived from elsewhere.

An alternative embodiment for accommodating selective polarizations in astaggered-frequency system is shown in FIG. 3(E) and FIG. 4. Servicefrequency filter 57 comprises a pair of individual bandpass filters 150,151. Filter 150 has a passband characteristic 140 with a centerfrequency 142 preferably approximately centered within the transponderband (e.g. 112) of a first polarization (e.g. LHCP). The second filter151 has a passband characteristic 141 with a center frequency 143corresponding to the approximate center of a transponder band (e.g. 113)in the alternate polarization (e.g. RHCP). Although it is preferable forthe filter passbands to be approximately centered within transponderbands, it should be understood that this is not essential so long as thepassbands fall within the transponder bands. The filter characteristicsare shown aligned with the adjacent LHCP and RHCP transponder bands.This is the preferred implementation in order to reduce the impact ofany variation in the gain of the system over frequency. However, it isnot necessary that adjacent bands be utilized, and any LHCP and RHCPband or bands could alternatively be selected. More than one may beused, with the signals either combined (for greater total signal) oraveraged. When two or more are used and averaged, the resulting systemis tolerant of the loss of a transponder, without adjustment. Thespecific filter characteristics and passbands are not critical, althoughthey preferably fall within the transponder bands with minimal or noinclusion of noise signals in the guard bands. 6 MHz filters may be usedfor convenience, or filters having a wider passband (e.g. 20 MHz with arolloff of −25 db at ±12 MHz) may be used to pass more received power.As with the previous embodiment, the noise component may be filteredpreferably above or below the signal band (e.g. 145).

Referring again to FIG. 4 and to FIG. 2, the signal 23 may be providedto a switch 160 whose outputs are in turn connected to filters 150, 151.The state of switch 160 is determined by a select input 161, whichpreferably corresponds to the LNB control signal for selecting RHCP orLHCP output. In known systems, a first DC voltage level (e.g. 13 volts)is provided for a first polarization state, and a second DC voltagelevel (e.g. 17 volts) is provided for the alternate polarization state.These DC voltages provide control inputs to the LNB for selecting LHCPor RHCP output, and provide power to the LNB electronics. In a preferredembodiment, the same control voltages are utilized by the lock-detectsubsystem 55 for determining the state of switch 160, and also forproviding necessary power to the circuits of the device.

Although the foregoing specific embodiments illustrate operation of thepresent invention by utilization of certain frequencies, it should beunderstood that other signal and/or noise frequencies may alternativelybe utilized.

Referring again to FIG. 2, the service frequency component is outputfrom the filter 57 and supplied to the RF detector 64 for e.g. voltageconversion before being fed to summer 59, while the noise frequencycomponent output from the filter 58 is fed to RF detector 65. The RFdetectors may comprise any known devices and methods for generatingoutputs which are proportional to the power level of the input RFsignals. Although simple analog components are preferred, digital orhybrid analog/digital circuits may alternatively be used. For example,the detectors may comprise A/D converters to convert the detected DClevels to digital format for subsequent processing.

In the preferred embodiment illustrated, one of the detected DC voltagelevels (preferably corresponding to noise signals) is inverted byinverter 68, and supplied to the adder circuit 59. The summer 59 sumsthe voltage data and outputs a difference signal level or value atoutput 66. Alternatives may likewise be utilized for generating anoutput proportional to the difference between the respective RF powerlevels. For example, a voltage subtractor may be used in place of theinverter and adder. If digital conversion is used, a digital adder orsubtractor may be used, or a microprocessor may determine the desireddifference value.

The output indicative of the power difference is supplied, in apreferred embodiment, to a pair of step function comparators 60 and 61.The comparators 60 and 61 evaluate the difference in power levels of thesignal and noise components. The comparator 60 determines whether thevalue is greater than a satellite signal loss threshold, which may beinput 40 or otherwise provided. The satellite signal loss threshold ispreferably settable and set sufficiently above the noise floor torepresent the minimum signal level at which an acceptable satellite lockmay be achieved in a given system, is setup, and location. The receivedsignal strength in a typical DBS system will vary from one region toanother, and may be influenced by antenna location, installation andother variable factors. It is therefore preferable to have a lockthreshold that can be adjusted to match the specific performancestandards for a given installation.

The other comparator 61 in turn determines whether the value is greaterthan an intermediate threshold which may be input 41 or otherwiseprovided. The intermediate threshold is set sufficiently above both thenoise floor and the signal loss threshold. The intermediate thresholdpreferably represents an intermediate signal strength level at whichsecure satellite lock is achieved. Other thresholds may also beprovided, above or below the lock threshold. If digital conversion isused, the comparator(s) may comprise any known hardware orsoftware-implemented comparison or difference detection.

The comparator(s) may be provided with fixed thresholds selected, e.g.,to represent a state of degraded performance or of signal loss. Thethresholds may be preset for certain locations or configurations, ornormal operating conditions. In general, the signal to noise (S/N) ratioat the lock/unlock threshold will be independent of geographic location.It may nevertheless be desirable to have adjustable thresholds, topermit optimization for e.g. a particular receiver.

It may also be particularly beneficial to have adjustable intermediatethreshold(s) which can be set, preset, or adjusted for optimum operationin a particular location. For example, where the received signalstrength is higher, it may be desirable to set a higher intermediatethreshold to provide maximum warning of an impending loss of signal.However, where the clear sky received signal strength is lower, the sameintermediate threshold may result in an excessive number of “falsealarms”, and a lower intermediate threshold (closer to the loss of lockthreshold) may be appropriate.

In particular embodiments, different thresholds may be utilized fordifferent transponders within the assigned spectrum. By way of example,one known commercial DBS system utilizes 16 high power transponderstransmitting at 240 watts, and 16 lower powered transmitters at 120watts. The S/N ratio differs for the low and high powered transponders.To permit optimized operation, appropriate thresholds can be useddepending on the nature (e.g. power) of a transponder whose signal isbeing utilized. In these embodiments, of course, it is necessary to knowwhich transponder the IRD is tuned to. In systems where the low/highpower status of the transponders corresponds to the LNB polarizationstates (e.g. where all LHCP signals are broadcast by low powertransponders, and all RHCP. signals are broadcast by high powertransponders), the polarizafion-select DC voltage may be used to alsoselect appropriate thresholds. Other control signals or schemes couldalternatively be used. In other embodiments, a single threshold (e.g.high power threshold) may be used for both transponders, providingadequate operation for many applications.

The comparators 60, 61 may be provided with external threshold inputs40, 41. The thresholds may be generated by a threshold generator 42. Inembodiments where comparators 60, 61 are analog devices, thresholds 40,41 may be voltage levels output by the threshold generator 42. Inpreferred embodiments, threshold generator 42 provides adjustablethreshold(s), and may comprise a manually adjustable trim resistor orresistor array. In this manner, manual adjustments can be made to tailorthe device operation to a given region, equipment or installation.

In other embodiments, a D/A converter may be used. One or more digitalwords may then be input 44 from a source 43. The source 43 may comprisea predetermined memory (e.g. ROM) or variable memory (e.g. RAM or binarydip switches). In certain embodiments, the threshold values may bedownlinked directly from the satellite 15 and stored in a buffer ormemory. In particular embodiments, the threshold value may be adjustedby means of an on-screen user interface (e.g. by providing thresholdgenerator 42 with suitable means for receiving signals from the userinterface or associated circuits). Combinations are also possible. Forexample, a threshold value may be downlinked to the lock detector 92 andstored in memory 43, then later adjusted (e.g. incremented ordecremented) by local adjustment (e.g. manual inputs via the userinterface). Further, the thresholds may be adaptive relative to otherinputs. For example, some (e.g. the intermediate) or all of thethresholds may be adjusted when temperatures fall below certain levels,to render the device more sensitive to reductions in signal strengththat may be caused by temperature-related conditions (e.g. iceaccumulation).

Where a plurality of detectors are utilized, each having a threshold,one or more of the thresholds may be derived from other(s) of thethresholds. For example, a first threshold value can be provided fromsatellite 15, input manually, or read from a memory or other source,e.g. 43. The other threshold value(s) may then be derived from the firstthreshold, for example, as a certain percentage or other function of thefirst threshold.

Some or all of the thresholds can also be region-specific in that thelocally stored or the downloaded threshold is dependent on the zip codeor other indicator (e.g. latitude and longitude) of where the IRD isinstalled. In one preferred embodiment, threshold values may be storedin memory corresponding to individual or preferably groups of zip codes.Other regional or geographic correlations may similarly be utilized toselect desired thresholds for different geographic regions.

The comparators 60 and 61 generate control voltages or other signalsthat represent the result of each comparison operation. The controlsignals are present on outputs 93 and 94. By way of example, a firstlevel voltage at the output 93 may indicate that the satellite signal isnot locked, or has fallen below the satellite signal loss threshold. Afirst level voltage at output 94 may indicate that the satellite signalhas fallen below the intermediate threshold and is approaching thesatellite signal loss threshold. This output 94 voltage may serve towarn users or the logic 53 of potential loss of the signal. Additionalcomparators may be utilized to give the lock-detector the capability toimplement additional thresholds.

The control signals output at 93 and 94 from comparators 60 and 61 canhave many advantageous uses in a satellite system such as a DBS receiversystem, other than providing signal “lock” information to logic 53. Forexample, the outputs from comparators 60 and 61 may issue commands viaan output link such as switch unit 71 or directly to another externaldevice 75. The lock-detect apparatus 92 can thus automatically activate,for example, a corrective cycle to melt accumulated ice or snow which isdegrading reception in response to degrading signal conditions. Becausethe apparatus 92 may operate independently of the receiving apparatus,such as IRD 95, the receiving apparatus need not be operating in orderfor the apparatus 92 and external device (e.g. heater) to operate.

Referring now to FIGS. 2 and 5, the output(s) of the comparators may befurther linked to a user interface generator 72. The generator 72 inturn has a feed line 69 linked directly to cable 29, which, as describedpreviously, is linked to the IRD 95 and television set 79. The directoutput 66 from the summer 59 may also be linked via output 98 to theinterface generator 72, to provide a difference signal value output 66for use in signal strength calculations in a generated signal strengthmeter.

Upon detecting a signal (e.g. from switch unit 71 or logic 53, ordirectly from outputs 93 and/or 94) indicating signal degradation, theinterface generator 72, through conventional means known in the art,sends a signal through the cable 29 to the IRD 95. The IRD 95 in turnpreferably causes a visual or aural response, such as a small icon 81,to be generated by the television set 79 or the IRD itself.

The user can then use a remote control (not shown) to cause thegenerator 72 to control a user interface, preferably an on-screen userinterface, such as shown in FIG. 5, through conventional means known inthe art. This user interface 85 preferably comprises a menu 80 toexplain to the user the various options 83 available to correct thedegradation of the satellite signal. In one particular example relatedto snow or ice accumulation, an antenna heater can be activated bychoosing its respective menu option or otherwise. In another embodiment,a realignment means or boresighter, such as an antenna rotor, can beactivated. In certain embodiments, once the selected external device,such as device(s) 75-77, has been activated through the user interface85, the selected device(s) 75-77 may cause the user interface generator72 to reset. The generated menu 80 and icon 81 are thus removed from thescreen. In the meantime, the satellite lock detector 92 may continue tomonitor the incoming signal from the LNB 20, and may cause the generator72 to generate the icon 81 again if the corrective device is notsuccessful in improving the satellite signal strength. Many other usesand options are likewise possible.

Preferably, the present embodiment of the lock detector 92 is adaptedfor use with a variety of systems such as DBS direct-to-home satellitereceiver systems. For example, a user may purchase the lock detectoralone as an accessory, or in combination with e.g. a satellite dishantenna heater, and retrofit the system to an existing DBS system. Thelock-detect device preferably may be installed in any easily accessiblearea between the LNB and the indoor IRD unit. The methods and apparatusmay also be employed in other RF transmission systems, such as LMDs,MMDs or other terrestrial broadcast services whose signals may bedegraded by environmental factors.

Although lock detector 92, interface unit 72, and IRD 95 are shown asseparate units, it should be understood that in certain embodiments someor all of these elements may be combined.

The method and system for satellite lock-detect described herein allowsthe system subscriber to conveniently determine when the satellitedownlink signal at the antenna has degraded to a particular point,including (but not limited to) a point that the signal may be completelylost upon further attenuation. By warning the subscriber of theseconditions around the antenna, the subscriber can take corrective stepsbefore the signal is completely lost, or be informed of automaticcorrective steps taken by logic 53.

Because the components of the unit in certain embodiments are relativelysimple and easy to implement logic functions, expensive microprocessorsare not needed although they may be utilized. Furthermore, becausecertain embodiments of the lock detector system described hereinpreferably are mounted in-line and separate from the receiving deviceitself and do not require analysis of the received information content,the receiving device need not be turned on for the system to operate,and the system operates independently of the information encoding orprotocols used.

Of course, it should be understood that a wide range of changes andmodifications can be made to the embodiments described above. It istherefore intended that the foregoing detailed description be regardedas illustrative rather than limiting and that it be understood that itis the following claims, including all equivalents, which are intendedto define the scope of this invention.

What is claimed is:
 1. A method of detecting a satellite signal having anoise frequency component and a service frequency component, said methodcomprising: establishing at least a first threshold value associatedwith an incipient loss of signal lock; developing a first valueindicative of the noise frequency component, and a second valueindicative of the service frequency component from the satellite signal,wherein the noise frequency component and the service frequencycomponent are spectrally separate; deriving a difference signal valuefrom said first and second values; comparing the difference signal valuewith said at least a first threshold value; and generating a firstoutput if the difference signal value differs from said at least a firstthreshold value in a predetermined manner.
 2. The method as recited inclaim 1 wherein said noise frequency component and said servicefrequency component are obtained by bandpass filtering portions of saidsatellite signal.
 3. The method as recited in claim 2 wherein said stepof deriving a difference signal value comprises the steps of: invertingone of said first and second values to obtain an inverted value; andsumming said inverted value with the other of said first and secondvalues to obtain a value indicative of the difference between said firstand second values.
 4. The method as recited in claim 3 furthercomprising the steps of: establishing a second threshold value differentfrom said first threshold value; comparing the difference signal valuewith said second threshold value; and generating a second output if thedifference signal value differs from said second threshold value in apredetermined manner.
 5. The method as recited in claim 4 wherein thestep of generating a second output further comprises the step ofcommanding a user interface to indicate that the satellite signal isdegrading.
 6. The method as recited in claim 5 wherein the step ofgenerating a first output value further comprises commanding a userinterface to indicate that the satellite signal has been lost.
 7. Themethod as recited in claim 4 wherein the step of generating a secondoutput further comprises the step of activating a peripheral device. 8.The method as recited in claim 7 wherein the step of generating a firstoutput further comprises activating a second peripheral device.
 9. Themethod as recited in claim 4 wherein said first threshold value isadaptive.
 10. The method as recited in claim 4 wherein said firstthreshold value is adaptive.
 11. The method as recited in claim 2wherein said step of deriving a difference signal value comprises thesteps of: converting the noise frequency component to a noise frequencyvoltage value which is proportional to the power level of the noisefrequency component; converting the service frequency component to aservice frequency voltage value which is proportional to the power levelof the service frequency component; inverting one of said voltage valuesto obtain an inverted voltage value; and summing the inverted voltagevalue with the other of said voltage values to output a signal valuerepresentative of the difference in the power levels of said components.12. The method as recited in claim 1 further comprising the step of, inresponse to at least said first output, generating a user interfacehaving a plurality of options for increasing the power of said servicefrequency component.
 13. The method as recited in claim 1 wherein saidnoise frequency component comprises at least predominantly noisesignals, and wherein said service frequency component comprises at leastpredominantly service signals.
 14. The method as recited in claim 13wherein said satellite signal comprises a plurality of transpondersignals having different characteristics, and where the steps ofdeveloping a first value comprises the step of a developing said firstvalue from a transponder signal having a same characteristic as that ofthe transponder signal being processed by a receiving device.
 15. Themethod as recited in claim 1 wherein said first threshold value isselectable.
 16. The method as recited in claim 1 wherein said firstthreshold value is adaptive.
 17. The method as recited in claim 1wherein the step of generating a first output further comprises the stepof activating a peripheral device.
 18. A method of monitoring thestrength of a received satellite signal presented to a decoder, saidsignal having at least one noise component and at least one signalcomponent, wherein the noise component and the signal component arespectrally separate, said method comprising: deriving from said noiseand signal components a derived signal value; comparing said derivedsignal value to at least one predetermined value associated with anincipient loss of signal lock; and generating an output if said derivedsignal value differs from said predetermined value in a predeterminedmanner.
 19. The method as recited in claim 18 wherein said derivedsignal value comprises a difference signal value, said predeterminedvalue comprises a predetermined threshold, and wherein the step ofcomparing further comprises comparing said difference signal value tosaid predetermined threshold.
 20. The method as recited in claim 19wherein the step of generating an output further comprises generating avisual or aural warning to a user via a user interface.
 21. The methodas recited in claim 20 further comprising the step of prompting the userto select from a menu of options presented by said user interface. 22.The method as recited in claim 21 wherein said user interface comprisesa screen image for display on a videoscreen.
 23. The method as recitedin claim 19 wherein said method is carried out whether or not saiddecoder is operating.
 24. A system for receiving a satellite signalhaving a predominantly noise frequency component and a predominantlysignal frequency component, wherein the noise frequency component andthe signal frequency component are spectrally separate, said systemcomprising: a satellite receiving antenna and low noise block; logic incommunication with said low noise block for processing said noise andfrequency components to obtain a derived signal value and comparing saidvalue to a predetermined threshold associated with an incipient loss ofsignal lock; and a user interface linked to said logic and at least oneexternal device and activated when said derived signal value differsfrom said predetermined threshold in a predetermined manner.
 25. Thesystem as recited in claim 24 wherein said user interface provides awarning when said comparison indicates that satellite signal lock hasbeen lost.
 26. A system for detecting a satellite signal, said systemcomprising: at least a first filter that isolates a predominantly noisefrequency component from said satellite signal; at least a second filterthat isolates a predominantly service frequency component from saidsatellite signal, wherein the service frequency component is spectrallyseparate from the noise frequency component; circuits that derive avalue indicative of a difference between the power levels of said noisefrequency component and said service frequency component to output adifference value; and circuits that determine whether said differencevalue is greater or less than a first threshold value associated with anincipient loss of signal lock.
 27. The system as recited in claim 26further comprising circuits that determine whether the difference valueis greater than a second threshold value.
 28. The system as recited inclaim 27 wherein said first threshold value further comprises a valuerepresenting a minimum signal level for acceptable operation of areceiver.
 29. The system as recited in claim 28 wherein said secondthreshold value further comprises a value chosen to represent a signallevel greater than said minimum signal level.
 30. A system for receivinga satellite signal from a satellite, the system comprising: a satelliteantenna; a subsystem that detects the satellite signal including aplurality of filters that isolate spectrally separate componentsindicative of the signal, logic that calculates a difference signallevel from the components, at least one comparator that determineswhether the difference signal level is greater than a threshold levelassociated with an incipient loss of signal lock; and a satellite signaldecoder linked to the satellite antenna by the subsystem.
 31. The systemas recited in claim 30 wherein said threshold level is manuallyadjustable.
 32. The system as recited in claim 31, wherein saidthreshold level is downloadable via said satellite.
 33. An accessorydevice for use with a satellite receiving station, said devicecomprising: at least one filter that isolates a predominantly servicefrequency component from a satellite signal received in said receivingstation; at least a second filter that isolates a predominantly noisefrequency component from said satellite signal, wherein the noisefrequency component is spectrally separate from the service frequencycomponent; circuits for determining a power value for the outputs ofsaid first and second filters; and at least one detector that determineswhether a difference level derived from the outputs of said powerdetermining circuits is above or below a threshold associated with anincipient loss of signal lock.
 34. The device of claim 33, furthercomprising logic in communication with said detector, said logictriggering a peripheral device.
 35. The device as recited in claim 34wherein said peripheral device comprises a user interface generator.